Millions of Americans must work at night and sleep during the day. Estimates for 1997 by the Bureau of the Census indicate that 16.8 percent of full-time workers are shiftworkers, including 3.5 percent working steady night shift and 2.9 percent working rotating shifts. Despite negative consequences on health, safety, and work performance, night work is necessary in a variety of occupations including health services, public safety, communications, transportation, the military, and manufacturing industries that require 24-hour operation for economic reasons. Night work is associated with disturbed sleep, impaired alertness, decreased performance, and increased accidents, including transportation and industrial disasters. These detrimental effects are largely caused by: 1) the desynchrony between circadian sleep tendency and the schedule of sleep and wakefulness required by night work, and 2) cumulative sleep deprivation. The National Occupational Research Agenda identifies "demanding work schedules, sleep disorders, and the risk of occupational illness and injury" as a prioity area. The proposed research assesses two practical interventions to counter the effects of night work, i.e., napping and caffeine administration. In limited prior research, both caffeine and napping have shown significant potential as effective interventions and both are feasible for immediate implementation by large numbers of actual shiftworkers, regardless of industry or specific job duties. Specifically, two nap schedules, caffeine, and a combination of napping and caffeine will be studied. Objective physiologic and behavioral measures of alertness and performance at night, and sleep quantity and quality during the day, will be used to determine the most effective intervention in laboratory studies of simulated shiftwork. The most effective intervention will be tested with actual shiftworkers in the field using quantitative measures of performance, alertness, and sleep. The results of the experiments in this designated priority research area will directly lead to specific night work intervention strategies that can be readily applied in a variety of industries.